A total of 132 asymptomatic Western blot (WB)+, 62 EIA+/WB-, and 8 EIA+/WB indeterminate donors have been enrolled in a 5-year prospective study. The source of HIV exposure was homosexual activity, 68% (83% of males); heterosexual contact, 28% (96% of females); IV drugs, 3%; transfusion, 2%; unknown, 6%. Compared with the WB- controls, WB+ donors were more frequently black (59 vs. 7%), male (82 vs. 57%), young (mean age 32 vs. 40), first-time donors (26 vs. 7%), and have a history of venereal disease (52 vs. 8%). The ratio of high to low risk WB+ donors decreased from 5:1 to 1:1 during the first 20 months of the study. On initial evaluation, WB+ donors were significantly more likely than WB- donors to have T4 cells <400/uL (39 vs. 7%) T4/T8 ratio <0.8 (68 vs. 3%), IgG >1.8 g/dL (48 vs. 2%), and positive anti-HBc (55 vs. 2%). Diminished responses to tetanus, PWM, and PHA were seen in 46, 38, and 18% of WB+, vs. 7, 18, and 4% of WB- donors. By l year of follow-up, 11% of WB+ individuals had abnormal responses to all 3 mitogens; by 18 months, 16% had T4 <100/uL and 20% had T4/T8 <0.2. HIV was isolated from 32 of 98 (33%) WB+ donors on at least one visit. Fifty-eight percent of WB+ donors were initially in CDC group II; 22 of 66 (33%) of these subsequently developed lymphadenopathy. Fifteen of 132 (11%) progressed to CDC IV; 5 developed thrush, 5 pneumocystis, 1 tuberculosis, and 4 constitutional disease. None of 70 EIA+/WB- or indeterminate donors were in HIV risk groups and one had evidence of HIV- related immune dysfunction or positive viral cultures.